The presently described embodiments relate to a method and apparatus for reducing intercolor bleed to improve print quality. It finds particular application in addressing intercolor bleed problems and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiment is also amenable to other like applications.
For color ink jet printers which print on plain paper, one of the challenges is to achieve a proper balance in ink properties which allows penetration into the paper at a sufficiently rapid rate so that pools of different colored inks in adjacent areas do not appreciably intermix. This phenomenon of intermixing is often referred to as intercolor bleed. However, this penetration of ink should not occur so rapidly so as to allow edge sharpness to be dominated by a random pattern of paper fibers. Typically, it is preferable to formulate the cyan, magenta, and yellow inks using penetrants or surfactants as constituents to enable penetration into the paper within less than a second, i.e., so that ink at the surface is no longer substantially mobile. For sharp black text and high optical density in black printing, however, it is preferable to formulate the black ink so that it less rapidly penetrates (e.g., penetrates in seconds to tens of seconds). This is called medium dry black ink.
Intercolor bleed is most noticeable for images which contain sharply defined borders between two patches of ink of different colors. Such patterns frequently occur in business graphics, for example. When intercolor bleed occurs, instead of the desired sharply defined border, the border appears ragged and fuzzy.
Typically, the target diameter of each spot in an ink jet print is approximately the square root of two times the pixel spacing for the case where all drop ejectors for a given color print nominally the same sized spot. This is to ensure overlap of diagonally adjacent spots. One implication is that at a color boundary, the adjacent different colored pixels will overlap to some extent. Some amount of mixing and intercolor bleed is thus inevitable, unless special measures such as pixel or drop deletion are taken.
Countermeasures against intercolor bleed include techniques for altering the image by deleting pixels or printed drops at the borders between colors. This gives the two adjacent patches a relief zone so that wet pools are less likely to come into contact and intermix.
In this regard, several patents teach various pixel modification algorithms to minimize intercolor bleed. For example, U.S. Pat. No. 6,361,144 to Torpey et al. relates to a method for processing color image data to reduce intercolor bleeding in an image printed on a receiving medium. U.S. Pat. No. 6,290,330 to Torpey et al. relates to a method of processing color image data for printing in an ink jet printer to maintain edge quality in an image recorded on a receiving medium. U.S. Pat. No. 6,183,062 to Curtis et al. provides a method for processing color image data to maintain edge quality in an image recorded on a receiving medium. In addition, U.S. Pat. No. 6,343,847 to Torpey et al. relates to a method for processing color image data to determine if a target pixel is within a border region near an interface. All of these patents are incorporated herein by reference.
However, printing algorithms which perform pixel or drop deletion may produce undesirable printing artifacts on certain types of images, such as pictorial images. It has been demonstrated that pixel management algorithms work significantly better for spot sizes corresponding to printing resolutions of 400 spi and above.
In addition, printing using printheads having different sized nozzles is known. For example, U.S. Pat. No. 5,745,131, entitled “Gray Scale Ink Jet Printer” by G. Kneezel, W. Burger, S. Harrington, D. Ims, and J. Stephany, which is incorporated herein by reference, describes a pattern of laying down dots for gray scale in which a first array of ejectors deposits ink spots of a first size on a first grid pattern, and a second array of ejectors deposits ink spots of a second size on a second grid pattern which is offset from the first grid pattern. The two arrays are also fired in time such that placement of the different sized spots is also offset in the scan direction.
Other embodiments of this type of printhead are described in U.S. Pat. No. 6,402,280, entitled “Printhead with Close-Packed configuration of Alternating Sized Drop Ejectors” by G. Kneezel, D. Mantell, J. O'Neill, T. Tellier and S. Harrington and U.S. Pat. No. 6,375,294, entitled “Gray Scale Fluid Ejection System With Offset Grid Patterns of Different Size Spots” by G. Kneezel, both of which are incorporated herein by reference.
These techniques of printing different drop sizes (and others), however, do not directly address the problem of intercolor bleed in a border or edge region of a printed image.